Traveling wave time delay device having a magnetic field in the drift region different from that in the delay line regions



KANTOROWICZ 3,417,230 TRAVELING WAVE TIME DELAY DEVICE HAV A MAGNETIC FIELD IN THE DRIFT REGION DIFFERENT QM THAT IN THE DELAY LINE REGIONS Filed March 31, 1967 FIG! My 25 INVENTOR G. KANTOROWICZ BY Q 7,

ATTORNEY United States Patent Claims. (El. 3153.6)

ABSTRACT OF THE DISCLOSURE An electronic delay line with distributed input and output couplers and with a drift space therebetween, wherein crossed electric and magnetic fields are established along the path of a beam propagating in coupled relationship with the couplers and through the drift space, and wherein magnetic pole-pieces for producing said magnetic field are provided with either protrusions or depressions facing said drift space, thereby operating said drift space with a magnetic field having a strength different from the field operating said couplers, whereby insertion loss of the device is minimized.

Background 0 the invention My copending application Ser. No. 370,258, filed on May 26, 1964, now US. Patent 3,341,733, describes .an electronic delay line including a waveguide in which an electron beam, whose translation velocity can be varied, propagates through crossed electric and magnetic fields. Before entering the waveguide and after emerging therefrom the electron beam traverses input and output coupling devices, respectively, formed by delay line portions coupled to the beam which is also propagating through crossed fields. The velocity of the beam in the coupling devices is adjusted to be substantially equal, in a broad pass band, to the group velocity of the wave propagated by the delay line of the coupling devices. The delay line portions have a structure which will satisfy, at least approximately, the relationship where c is the speed of light, A is the Wavelength of the injected wave, corresponding to the middle of the pass band, h is the cyclotron wavelength corresponding to the gyromagnetic angular speed of the electrons about the lines of force of the field B, which angular speed is proportional to the intensity of the field, v is the phase velocity of the wave in the coupling devices, and 11 is the translation velocity of the beam in the coupling de' vices.

It is also indicated in the above-referenced co-pending application that the velocity of the beam in the waveguide may be controlled by adjusting either the magnetic field B or, preferably, the electric field E. To this effect, FIGURES 1 and 5 of the co-pending application show a means of varying E, while the magnetic field B is maintained at a fixed value, which is the same for the waveguide and for the space in the coupling devices.

This disposition causes the system to operate with a considerable insertion loss. Indeed, the insertion loss in- 3,417,280 Patented Dec. 17, 1968 creases with the number of wavelengths in the waveguide, corresponding to the passage of the signal through the entire length L of the waveguide which forms the drift space. This number N is given by the relation Since the term in parentheses is not zero, the number N has a certain non-zero value which determines the extent of the insertion loss.

Brief description of the invention In accordance with the invention, there is provided an electronic delay line including a vacuum tube having an evacuated enclosure in which is located an electrode system forming a drift space and having an input and an output, means for producing an electron beam and for directing said beam through said input into the drift space of the electrode system, collector means for collecting said beam after emerging from said electrode system output, means for establishing crossed transverse electric and magnetic fields along the path of said beam, a geometrically periodic delay line section extending at least along a portion of the path of said beam preceding said electrode system input, and means for energizing said delay line section with a microwave signal, the velocity of said beam being arranged to be substantially equal to the group velocity of the wave propagating in said delay line section, characterized in that said drift space is placed in a fixed transverse magnetic field having a strength different from that of the field in which is placed said line section, while the velocity of the beam is varied by varying the electric field.

More precisely, the magnetic field through the drift space is adjusted to such a value that the cyclotron wavelength in the drift space becomes equal to the middle wavelength of the pass-band.

This field adjustment may be effected by giving the magnet polepieces a suitable form, in particular, a form presenting a projection in the region of the drift space, for relatively increasing the field strength in that region when the coupling devices operate with a forward wave, as in FIGURE 1 of the above-referenced co-pending application; or on the other hand, the pole-pieces may have a form presenting a trough or pit in the region of the drift space for relatively reducing the field strength when the coupling devices operate with a backward wave, as in FIGURE 5 of the above-referred co-pending application.

In either case, h is made, at least very nearly, equal to A so that the term between parentheses in Equation 2 above becomes zero, and N=O, or at least very nearly zero. This means that the signal at the middle wavelength I frequency propagates in the drift space with an infinite phase velocity. On either side of the middle wavelength the ratio Mi remains very near to 1 so that the number N is very low in the entire pass-band. The device thus operates with an insertion loss which is greatly reduced in comparison to prior devices.

It is therefore an object of the present invention to provide an electronic delay line which entirely avoids, or otherwise substantially eliminates, the difficulties inherent in known arrangements of a similar nature.

It is another object of the invention to provide an electronic delay line having a reduced insertion loss.

It is a further object of the present invention to provide an electronic delay line having reduced insertion loss which is achieved by simple and very economical means.

These and other objects, features and advantages of the present invention will become more apparent from the following detailed description thereof when taken in connection with the accompanying drawing which illustrates two exemplary embodiments of the present invention and wherein:

FIGURE 1 is a longitudinal section of the electronic delay line shown in FIGURE 1 of U.S. Patent 3,341,733;

FIGURE 2 is a partial schematic view of the tube illustrated in FIGURE I placed between pole-pieces profiled in accordance with the present invention; and

FIGURE 3 is a bottom plane schematic view of the tube illustrated in FIGURE of the above-referenced US. Patent 3,341,733, placed between pole-pieces profiled in accordance with the present invention.

Specific description of the invention Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGURE 1, the electronic delay line illustrated therein corresponds to the tube illustrated in FIGURE 1 of the above-referenced co-pending application, which is constituted by a tube compricing, within an evacuate envelope 1: a cathode 2 emitting electrons forming a beam 3; an electron-optical system comprising an anode 4 and a negative electrode 5 for directing the beam in the longitudinal direction of the tube; a negative electrode 6, commonly referred to as sole, placed parallel to the beam 3; a first delay circuit portion 7 carried at the anode potential and facing the first portion of the sole 6 on the other side of the beam 3; a positive electrode 8 facing the second portion of the sole 6 and separated galvanically from the circuit 7; a second delay circuit portion 9 facing the third portion of the sole 6 on the other side of the beam 3, separated galvanically from the electrode 8 and carried at the anode potential; and a collector 10 placed at the end of the path of the beam 3,

The input of the delay circuit portion 7 and the output of the delay circuit portion 9 are connected respectively to the coupling devices 11 and 12 of the tube, constituting respectively the input and the output of the electronic delay line.

A transverse magnetic field of which the lines of force are indicated by the circles 13, is furnished in accordance with the present invention, described in connection with FIGURES 2 and 3, to traverse the inter-electrode space of the tube.

Suitable potentials are applied to the different connections 14, 15, 16, 17, 19, of the electrodes 2, 5, 6, 10, 7, 9 of the tube, to establith within the inter-electrode space a transverse electric field E, defining at the same time as the magnetic fi-eld B, the translation velocity of the beam V =E/B, and to permit the production, the concentration and propagation of this beam between the cathode 2 and the collector 10. An adjustable potential is applied by way of the terminal 18 and the rheostat 21 to the electrode 8 to enable adjustment of the translatory velocity v within the space between the electrodes 6 and 8.

It is desired that section 8 be placed in a magnetic field B which is not equal to the operating field B of sections 7 and 9. This field must be such that the cyclotrons wavelength h in section 8 is equal to the middle wavelength propagating in sections 7 and 9. Recalling that the coupling devices of FIGURE I operate with forward waves and that this device functions with 7\ it is thereforenecessary to reduce t in section 8 in order to make it equal to A.

Since the cyclotron wavelength varies in inverse ratio to the magnetic field, it is consequently necessary to increase the field B with regard to B This is obtained in accordance with the present invention, as seen in FIG- URE 2, by providing each one of the pole-pieces 24 and 25 providing the magnetic field for the tube with a projection or protruzion 26 and 27, respectively, within the limits of section 8, shown schematically in the figure along with sections 7 and 9. For the example considered in the above-referenced application where the ratio MA is 0.9 and the field B is 1070 gauss, the profile must be such that the field B =1070/0.9==1190 gauss.

In a similar manner FIGURE 3 represents schematically the tube of FIGURE 5 of the above-referenced co-pending application, as seen from the bottom. Sections 8, 7 and 9 correspond respectively, as in the preceding case, to the spaces between electrodes 86, 76 and 9-6 of the referenced device. However, unlike the device of FIGURE 1 of the present application, the coupling devices in this embodiment operate as indicated in the referenced application with a backward wave, and the device functions with A in sections 7 and 9. To make A equal to in the drift space, it therefore is necessary to increase h that is reduce B with respect to B The pole-pieces 24 and 25 are therefore provided with troughs 28 and 29, respectively, within the limits of section 8. Taking again the exemplary parameters in the co-pending application wherein A =8 cm. and )\=10 cm., it is found =1.25. With B =1340 gauss, the pieces 24 and 25 should be profiled in such a way that B =1340/1.25=10 72 gauss.

It will be noted that the dimensioning indicated could be realized only approximately with reasonable tolerances with no other result than a slight displacement of the wavelength corresponding to the minimum of insertion loss with regard to the middle Wavelength. On the other hand, the de:ired modification of the magnetic field in certain regions of the device may be realized by any means accessible to those skilled in the art within the scope of the appended claims.

I claim:

1. In an electronic delay line including a vacuum tube having an evacuated enclosure in which is located an electrode system forming a drift space and having an input and an output, means for producing an electron beam and for directing said beam through said input into said electrode system, collector means for said beam emerging from said electrode system output, means for establishing a transverse electric field along the path of said beam, a

first geometrically periodic delay line section extending at field and said beam path having a strength in said drift space different from that provided in said delay line section.

2. A delay line as claimed in claim 1, wherein the magnetic field through the drift space is adjusted to a value wherein the cyclotron wavelength in the drift space is substantially equal to the middle wavelength of the passband of the delay line.

3. A delay line as claimed in claim 1, including a second geometrically periodic delay line section extending along a portion of the path of said beam between said electrode system output and said collector means, and signal output means coupled to said second section for extracting the delayed signal therefrom, wherein said second section is positioned in the fixed magnetic field of said magnetic field generating means having substantially the same strength as the field in said input delay line section.

4. An electronic delay line as claimed in claim 1, in-

5 6 eluding means for propagating through said coupling References Cited means a microwave signal in a forward mode, and where- UNI-[ED STATES PATENTS in magnetic field generating means include opposing poleh h 0 f b d a 2,811,664 10/1957 Kazan 315-3.6 plefzes z z a P ace em 0 l e a PLOJECUOH 3OS6069 9/1962 Parain famg space- I 3,179,838 4/1955 Adler 315 3 An le r nic delay as claimed in claim 1, in- 3 Adler eluding means for propagating through said coupling HERMAN KARL SAALBACH Primary Examiner means a microwave signal in a backward mode, and

wherein magnetic field generating means include opposing CHATMON Assiflmlt Examiner pole-pieces each having a pole face embodying a recess 10 us facing said drift space. 31539.3; 335-210 

